Sure people that own offsite book at WDW, but so do WDW resort owners book at the offsite resorts. The offsite resorts are also at high demand, so they offset each other IMO.
Ideally, but I suspect far less that balanced in reality. Especially since the appeal of Hilton Head in February is not high, nor the Florida Beach in January. Those locations are not year round draws and the members who own them to stay there tend to book their vacations during their ownership window - making Summer a difficult time to get those resorts at seven months. And then a certain number of people have bought those resorts because they were the cheapest resale (ignoring dues) in order to stay at Disney World - making the problem a little less balanced yet.
Aulani and Disneyland have year round appeal, but bring their own balance problems - GCV is too small for the number of WDW owning DVC members who want to go even once every ten years - with very few of the owners trading into WDW Resorts more often than staying "home" - and I suspect Aulani will have similar patterns - almost everyone wants to go to Hawaii at least once, but the owners there generally choice that resort because they are regulars. With far more members at WDW than Aulani, its going to be a hard resort to book.